As is well known, "steam floods or drives" are commonly used to recover heavy hydrocarbons, e.g. heavy, viscous oil, from subterranean reservoirs. In a typical steam flood, steam is injected through an injection well(s) and flows through the formation towards a separate, production well(s). The steam heats the oil and other formation fluids, reducing their resistance to flow by lowering the viscosity of the oil. In addition, the steam provides an additional driving force to increase the flow of oil and other formation fluids toward the production well(s) where the fluids are produced to the surface.
The wells used in steam floods, both the injection and the production wells are typically completed "open-hole" and then "gravel packed" to control the flow of sand and/or other particulate material from the producing formation into the wellbore. In a typical gravel pack completion, a slotted liner or the like is positioned in the wellbore adjacent the injection or production interval and is surrounded by "gravel" which, in turn, is sized to block the flow of particulate material therethrough while allowing the flow of fluids between the formation and the liner.
One of the most serious problems encountered in routine steam flood is the early breakthrough of steam at the production well. Due to the relative densities of the steam and the formation fluids, the steam tends to rise towards the top of the formation as it flows through the formation. This natural gravity segregation results in a less than 100% vertical sweep of steam through the formation and is likely to result in the steam breaking through into the production well from a zone which lies at or near the the upper end of the producing formation. Once breakthrough occurs, the injected steam will continue to take the "path of least resistance" along the swept, upper zone of the producing formation thereby continuing to bypass the unproduced, lower zones of the producing formation or interval which may lead to an early abandonment of the well wherein substantial amounts of oil remain unrecovered. Steam in the casing annulus can create excessive casing backpressure which reduces the inflow rate of oil into the wellbore. Steam breakthrough may also cause production downtime due to rod pump failure (pump galling, etc.) or stuffing box failure (excessive heat).
Several techniques have been proposed for controlling steam breakthrough in steam flood recovery operations. One is to merely redrill the production well when the steam breaks through and then set the well casing lower into the production interval to a point below the steam breakthrough zone thereby blocking off the upper zone of the producing interval which has experienced the steam breakthrough. Obviously, this technique is both time consuming and very expensive to carry out. Another known technique is to allow the fluid level in the production wellbore to build up above the level of the steam breakthrough zone. Again, this is expensive as it has been found to substantially reduce the oil production rate from the well. Another technique is to close the wellhead casing valve ( which may be connected to a wellhead casing vapor collection flowline system), thereby allowing the steam pressure to build up and create a backpressure on the steam breakthrough zone.
In other techniques, wells have been recompleted by either sidetracking a new liner in place or replacing the existing liner with a new liner wherein the new liner includes a blank section which will lie adjacent the steam zone when in place to prevent the steam from entering the liner. In each of these latter techniques, the completion interval which remains open to production is significantly reduced.
Recently, a technique has been developed wherein a resin is placed into the gravel surrounding the liner and set to block the flow of steam therethrough (e.g. see U.S. Pat. No. 5,215,147). While successful, this technique is expensive and is considered cost prohibitive where long steam breakthrough zones are involved. Also, the resin is difficult to place accurately in the wellbore and may, in some instances, seal off not only the steam intrusion zone but also a substantial portion of the production interval as well. Further, once the resin sets, it is difficult, if possible at all, to later retrieve the liner from the wellbore.